Wal-Mart Stores (WMT) is back atop the list of largest U.S. companies — perhaps with a boost from tough times.

The world's largest retailer unseated ExxonMobil(XOM) at the head of the annual Fortune 500 ranking, which was released Thursday. Falling oil and gasoline prices hurt Exxon, while consumers' growing need for low-priced necessities helped Wal-Mart.

The closely watched list, which ranks companies based on their 2009 revenue, was rife with evidence of the unsettled economy as homebuilders, automakers and energy companies slipped or disappeared in the ranking while recession-resistant industries such as health care rose.

And the ranking showed the sober reality of the companies' strategy to survive the downturn — cutting jobs and other costs to improve profits.

Fortune said the list shows the "long-awaited recovery is underway, but it's a slow painful slog".

Overall, total net income for companies on the list grew 350% for the year — the second-largest gain in the list's 56 years. But revenue for Fortune 500 companies fell 8.7% for the year, the largest percentage decline since 1983.

The Fortune 500 companies shed 821,000 jobs during the year, the biggest loss ever recorded by the list.

The top 10 mostly featured familiar players.

Wal-Mart has held the top seat on the ranking seven out the past nine years. Its 2009 revenue was $408 billion.

But a fall in commodity prices bumped Exxon down to its second-place position with revenue of $285 billion and cut at least six energy production, oil-refining and pipeline companies from the larger list.

There was a notable exception, as weak auto sales pushed General Motors with revenue of $105 million, from sixth place to 15th place. This is the first time in the list's history that GM did not make the top 10.

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